What is a ‘bomb cyclone’?

A “bomb cyclone” or “weather bomb” is an unofficial term for what is known as explosive cyclogenesis, according to BBC Weather.

This occurs when the central pressure of a low pressure system falls by 24 millibars in 24 hours and can result in violent winds developing around the system.

The winds can be strong enough to bring down trees and cause structural damage.

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The storm, the Washington Post adds, will “in many ways resemble a winter hurricane” which could be the eastern US’s most intense in decades.

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Media captionCold snap grips North America

Where is it expected to hit?

On Thursday and Friday, the major storm is expected to develop along the eastern seaboard of the US, bringing strong winds, rain, sleet and snow, according to BBC Weather.

The storm is forecast to undergo rapid cyclogenesis over the Atlantic Ocean, and current projections show areas north of New York as having the highest risk of significant impacts from strong winds and heavy snow.

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Media captionPeople around the US have rapidly been turning boiling water into snow

Major north-eastern cities such as Boston are at risk of blizzards, and it is expected to cause disruption at air travel hubs with power outages also possible.

Governors have issued states of emergency in Florida, Georgia, North Carolina and Virginia, and schools have been cancelled or delayed in several states.

New York City may see up to one foot (30cm) of snow fall, and similar or higher levels are expected throughout New England.

The US federal government delayed opening for two hours on Thursday.

Parts of Florida, including the northern city of Tallahassee, have already seen their first snow settling in decades.

Excited residents snapped photos of themselves playing in the snow, and school was cancelled in much of the state.

Is it cold everywhere?

No, it was actually colder in Jacksonville, Florida, than it was in Anchorage, Alaska, on Tuesday.